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Old 3rd January 2004, 09:40 PM   #1
lpd is offline lpd  Canada
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Default 6r-a8???

A friend of mine has a Sansui stereo tube amplifier with 6R-A8 outputs? This amplifier is great sounding, but we can't seem to locate output tubes for it. Anyone here seen these? Know where they can be purchased?
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Old 3rd January 2004, 10:15 PM   #2
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Hi,

Quote:
Anyone here seen these? Know where they can be purchased?
That's a typical Japanese tube...I don't know of any equivalents.

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Old 3rd January 2004, 10:25 PM   #3
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Here is the best listing i've found

http://w1.871.telia.com/~u87149905/hexodup/6ar8.htm

and the data sheet pdf.

$7 each at the TubeStore.

dave
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Old 3rd January 2004, 10:30 PM   #4
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Hi,

Quote:
Here is the best listing i've found
Afraid that's not the same tube, Dave...

The Japanese had a number of their own references and that Sansui tube is one of them...
Same trouble with some Luxman gear amongst others.

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Old 3rd January 2004, 10:51 PM   #5
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Quote:
Originally posted by fdegrove
Afraid that's not the same tube
That's gotta be confusing, having different tubes with the same designation

dave
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Old 3rd January 2004, 10:58 PM   #6
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Hi,

Quote:
That's gotta be confusing, having different tubes with the same designation
Tell me about it...To make it even worse almost none of these were exported except when inside the gear that is...

Pretty depressing but it had something to do with post WWII regulations, I think.

What sets the two types apart is that hyphen as far a nomenclature is concerned.

Too bad,
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Old 4th January 2004, 01:43 AM   #7
jun is offline jun  Japan
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Default Made a mistake for sending incomplete message

Made a mistake and sent the incomplete massage.
Sorry.
Hello everyone.

NEC 6R-A8 is an indirectly heated Triode 9pin mT tube (just like a EL84/6QB5).
Please note that this tube was designed by NEC (Nippon Electric Co.) and made "only" by NEC (no other tube manufacturers made this tube, Toshiba had the 6G-A4 that rivals 6R-A8 tube).
And this tube was originated from 6BK5, and the NEC modified it.
As a result, you can see that this tube has a screen grid internally connected to plate.
The characteristics of this tube are kind of a famous 2A3 with higher input sensitivity (i.e. similar plate resistance, higher gm, higher mu).
Now, this tube is a very grare itemh even in Japan.
I usually donft see it in catalog listing of almost any tube broker in Japan.
Even when I see it (once a year or so), the price is unbelievably high.
I know that NEC made this tube at least somewhere around 1980s (I remember I bought this tube when I was a kid).
So I donft think there was any export problems for this tube.
Lux used this tube for the Type 38 integrated Amp (they changed to 50A-C10 on later models) and used for their gKith amps.
These tubes popped-out when Japanese Tube makers stopped making 2A3, and have greater input sensitivity but unfortunately the linearity is not as good as the 2A3 (well most high gm tube have this tendency).
And since this tube was not so expensive, the material and construction is just as a normal tube in spite of having plate dissipation of 15 watts (and 6 watts for heater).
So you have to be careful to not overload this tube (it is a mT tube!) .
It does not use carbonized nickel plate or fancy glass envelope like the Bendix Red Bank tubes
Since it is almost impossible to obtain these tubes, and if the tube fails, the only way to salvage the amp is to modify it accept more popular tubes, but this is not easy.
Here is the Spec for this tube (may be useful).
Pin1 IC, Pin2 K, Pin3 G, Pin 4-5 H, Pin 6 G, pin 7-8 IC, Pin 9 P. (must leave IC open!, both grid pins must be connected for heat dissipation)
Max ratings
Eb=350V , Pp=15W, Ik=120mA, Ec1=-100Vmax, Rg=0.1(Fixed) 0.25Mohms(Self)
Heater 6.3V 1.0 A
Gm=10.5 (mA/V) rp=0.9Kohm, u=9.7
(Self Bias P-P) Eb=270V, Rk=260 ohms(for 2 tubes) RL=5K (p-p), eg1(g-g rms)30V
Ib=80 to 120 mA (2 tubes) Po=12Watts , KF=3%

Regards,
jun
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Old 4th January 2004, 01:47 AM   #8
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Hi,

------Oufti....Now we kow....

Cheers and thanks,

Sayomayonara,
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Old 22nd October 2004, 05:05 PM   #9
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Hi Jun,

I am using Luxkit A1020 with 4 of Nec 6a-r8 but I tried many time to buy another 6ar8 tube for my reserve.
Unfortunately if my tube is going to die what will I can do with the rest OPT ....remaining thing in my amplifier

What tube can I replace 6ar8 in the future or how can I modify it with Lux OY 14 OPT

Thanks in advance

Rgds,
Huy
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